1. Field of the Invention
The present invention relates to a scroll type compressor, and in particular, the present invention relates to a scroll type compressor having an improved counterweight and an improved drive bush.
2. Description of the Related Art
Scroll type compressors are known and disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 2-176179. In this compressor, a stationary scroll member comprising a stationary side plate and a stationary scroll portion integrally formed with the stationary side plate is arranged in a housing, and a movable scroll member comprising a movable side plate and a movable scroll portion integrally formed with the movable side plate is engaged with the stationary scroll member of 180 degrees out of phase from each other. A drive shaft is rotatably supported in the housing via a bearing, and has a larger diameter inner end portion with which a slide key is integrally formed to axially extend therefrom. The slide key has a first axis parallel to and offset from the longitudinal axis of the drive shaft. The slide key has a second axis perpendicular to the first axis and inclined relative to a line passing through the first axis of the slide key and the longitudinal axis of the drive shaft to the side reverse from the rotational direction of the drive shaft. A drive bush is slidably fit on the slide key so as to move along the second axis of the slide key. The drive bush carries the movable scroll member via a bearing and, in cooperation with rotation preventing means, causes the movable scroll member only to revolve around the longitudinal axis of the drive shaft. A counterweight is integrally formed with the drive shaft.
In this compressor, the rotation of the drive shaft is transferred to the movable scroll member via the slide key and the drive bush for causing the movable scroll member to revolve around the longitudinal axis of the drive shaft, whereby the compression chamber formed by the mating stationary and movable scroll members is gradually shifted toward the center of the scroll members, reducing the volume of the compression chamber, to thereby suck a refrigerating gas into the combustion chamber, compressing the gas in the combustion chamber and discharging the compressed gas from the combustion chamber.
The counterweight counterbalances the eccentric moment of the movable scroll member transferred to the drive shaft via the drive to accommodate the dynamic unbalance of the movable scroll member.
In addition, owing to the slidable fitting of the drive bush on the slide key, the drive bush is allowed to slidably move along the second axis of the slide key for adjusting or minimizing a clearance between the stationary and movable scroll members. That is, a seal between the stationary and movable scroll members is ensured, by urging the drive bush by a driving force of the drive shaft and a reaction force of the compressed gas. The drive bush can move along the second axis of the slide key in one direction by which the eccentricity between the longitudinal axis of the drive shaft and the longitudinal axis of the drive bush is increased and in the other direction by which the eccentricity is decreased. In the former case, the drive bush is moved so as to force the movable scroll member to the stationary scroll member. In the latter case, a clearance between the stationary and movable scroll members becomes large, and thus it is possible to avoid collisions of the scroll members with each other during the reversal motion of the movable scroll member when the compressor is stopped and when foreign matter is introduced in the compressor.
In the above described compressor, the counterweight is integrally formed with the larger diameter inner end portion of the drive shaft, and a problem arises in that fabricating and assembling steps of the compressor are complex.
Also, if the counterweight is integrally formed with the drive bush, fabricating and assembling steps of the compressor are also complex. In addition, the counterweight moves with the drive bush when the drive bush moves along the second axis of the slide key, and the stroke of the slidable movement is restricted by the consideration that the large counterweight does not interfere with the inner wall of the housing. In the case where the drive bush is moved in the direction by which the eccentricity is increased, there will be no problem if the stroke of the drive shaft is restricted to a small value since a good seal is ensured even at a small stroke in this instance. However, in the case where the drive bush is moved in the direction by which the eccentricity is decreased, it is preferable that the stroke of the drive bush is not restricted to a small value and is as large as possible to avoid possible damage of the stationary and movable scroll members when an excessive load is accidentally applied to the stationary and movable scroll members.